Jarrod Parker said his arm feels fine and that his confidence remains high.

But he added one other thing.

“Obviously,’’ the right-hander said, “I have to figure some things out.”

Most of the figuring after his outing Thursday night required a calculator: Parker’s ERA jumped to 8.10 after he gave up six runs in 5 1/3 innings during a 10-2 loss to the Baltimore Orioles.

In 23.1 innings this season, Parker has given up 21 runs, 37 hits and 13 walks.

As Manager Bob Melvin noted, there were times against the Orioles when he looked sharp. But when things went bad, they did so quickly. Parker saw it the same way. “Two, three, four pitches can make a difference,’’ he said. “That’s something that needs to change.”

Parker’s woes are part of a surprising trend for an A’s rotation that was so terrific a year ago.

A’s starters are 5-8 with a 6.12 ERA over the past 16 games and opponents are batting .306 against them during that span. Take Bartolo Colon out of that equation and the A’s rotation is 3-8 with a 7.44 ERA.

Melvin is optimistic that they will find the cure. But on this night?

“We had a stinker,’’ he said.

# # #

A few other notes courtesy of the A’s media relations staff:

— The A’s are 11-2 against the American League West and 2-8 against everyone else. They are 1-6 to start this 10-game stretch against the A.L East.

— Jed Lowrie went 1 for 3 to give him 31 hits this month. He needs two more to tie the Oakland record for most hits in April, a mark shared by Stan Javier (1994) and Ben Grieve (1998).

— The Orioles have won 101 consecutive regular-season games when leading after seven innings. According to the Elias Sports Bureau, that is the second longest streak for any team since 1961. (The 1998-99 Yankees had 116 straight).